Conventionally, seat suspensions are well known which are arranged to be maintained in a predetermined height level even when drivers of varying weights occupy a driving seat such as a truck cab and also which are provided between a seat and the floor surface of a car body so as to improve the comfortableness of the occupants of the seat. Such seat suspensions are designed to have an elastic property by means of a spring or pneumatic means and, accordingly, when driving a car in bad road conditions, such suspensions roll as the car body sways from side to side which impairs the comfort of the occupant. The elastic property may or may not be necessary depending on actual running road conditions or an occupant's preference. Also, the distance between the seat suspension and the steering wheel when the seat is occupied varies from that when unoccupied because of the elasticity of the seat suspension. In particular, in the unoccupied condition, the seat cushion is lifted up to narrow the distance. As a result, it is difficult for a person to climb in or out of the car smoothly.
In view of the above-mentioned drawbacks of the prior art seat suspensions, the present invention aims at providing a new seat suspension in which a lock mechanism is provided to lock the seat suspension in a desired height level and the locked height level can be adjusted in a plurality of steps.